1. Field of The Invention
The present invention relates to an actuating system for excavator, a kind of construction machinery, and more particularly to an automatic actuating system for actuators, such as a boom cylinder, a dipper cylinder, a bucket cylinder, a swing motor and a pair of travel motors, of the excavator capable of improving the operational effect of the actuators and the facility in controlling the actuators.
2. Description of The Prior Art
Conventionally, excavators are provided with a plurality of actuators which are actuated by hydraulic power and comprise a driving motor section comprising the swing motor for swinging an upper frame provided with a control cab with respect to a lower frame provided with travelling members, such as crawlers, and the travel motors for travelling the excavators, and an actuating cylinder section comprising the dipper cylinder for driving a dipper stick, the boom cylinder for driving a boom and the bucket cylinder for driving a bucket. The actuators are controlled by means of control levers/control pedals which are provided in the cab and handled by the operator in order to efficiently carry out several operations of the excavator such as excavating operations, surface finishing operations, loading operations and the like.
However, known excavators have the following disadvantages resulting in fatigue of the operator and occurrence of safety accident during operations carried out thereby.
First, there is a disadvantage in that the bucket of the excavator may become stuck or overloaded, such as by engaging a heavy rock, large volume of soil contained thereon or the like. In this case, the operators conventionally handle the control levers/pedals so as to actuate the actuating cylinders, such as the boom cylinder, the dipper cylinder and the bucket cylinder, to drive the overloaded bucket in opposite direction to the excavating direction so as to allow the overloaded bucket to be free from the overloaded state. However, an unskilled operator feels uneasiness because of shake of the excavator car body resulting from a shock imposed thereto due to the overloaded bucket so that he often controls the actuators to move more extent than the actuators need, thereby causing the operational efficiency of the excavator to be considerably deteriorated, while a skilled operator can efficiently handle the actuating cylinders to actuate the overloaded bucket to move backwards in a desired distance and then move up to a desired height, and also actuate the bucket to move in the excavating direction in order to continue the excavating operation under a desired condition without any overload.
Second, the control levers/pedals are handled by hands and feet of the operator at the same time during the operations by the excavator so that it needs skilled handling and careful attention of the operator. Especially, during excavating operation by the excavator, objects such as soil and the like which are excavated and contained in the bucket has to move without dropping thereof in order to be loaded in a truck or poured to another place. Thus, the operator pays careful attention in handling the control lever for the bucket cylinder simultaneously with handling another levers/pedals such as for the dipper cylinder, the boom cylinder, the swing motor or the travel motors in order to allow the open upper portion of the bucket to be parallel with or maintained at an angle with respect to the absolute horizontal line of earth. Thus, the known excavators have a disadvantage in that serious fatigue of the operator occurs in accordance with repeated excavating operation so that the excavating operation can not be continued for a long time, and furthermore in case of unskilled operator, the operational efficiency is deteriorated due to unskilled handling for the several control levers/pedals for actuating several actuators at the same time.
Third, the control levers and pedals are handled by hands and feet of the operator at the same time during the operations by the excavator so that it needs skilled handling and careful attention of the operator. Especially, during surface finishing operation by the excavator, the operator first handles the control lever for the bucket cylinder to cause the front tip or the bottom of the bucket to closely contact with the ground surface which is to be finished, and he then handles the control levers/pedals for actuating the dipper cylinder, the boom cylinder, the swing motor or the travel motors in order to carry out the desired surface finishing operation with respect to the ground surface. Thereafter, simultaneously with handling the levers/pedals for another actuators except for the bucket cylinder and the boom cylinder in order to carry out the surface finishing operation the operator has to handle the levers for the bucket cylinder and the boom cylinder to prevent the front tip or the bottom of the bucket from being separated from the ground surface during running of the excavator. Hence, the operator has to have skilled handling and pays careful attention in handling the lever for the bucket cylinder and the boom cylinder simultaneously with handling the levers/pedals for the dipper cylinder, the swing motor or the travel motors in order to carry out the surface finishing operation simultaneously with allowing the front tip or the bottom of the bucket to contact with the ground surface. In accordance, the known excavators have a disadvantage in that serious fatigue of the operator occurs in accordance with repeated surface finishing operation so that the excavating operation can not be continued for a long time, and furthermore it is very difficult to handle the control levers/pedals for several actuators at the same time.
Fourth, the known excavator has a disadvantage in that its actuators are overly driven in accordance with miss-handling of the control levers/pedals, thereby causing safety accidents such that actuating parts such as boom strikes neighboring constructions such as buildings while the swing motor is driven so as to swing the upper frame of the excavator with respect to the lower frame, and also the bucket in case of excavating operation unconsciously strikes underground constructions such as an underground water line, an underground wiring or an oil pipeline.
Fifth, The known excavators use the hydraulic fluid outputted from the hydraulic pumps for actuating a spool of a directional control valve for each actuator. If there is provided in the excavator only a hydraulic pump commonly connected to whole actuators, the pump must require a large capacity capable of efficient actuating the spools of the whole directional control valves at the same time as demanded. However, in case of requiring relatively lower hydraulic power due to requirement of actuating a part of actuators, considerable power loss occurs in the hydraulic pump due to driving the pump of large capacity even though there needs only low hydraulic power, thereby causing the driving power of the engine for driving the hydraulic pump to be unnecessarily required, thereby causing considerable power loss. Thus, the known excavators are generally provided with a parallel type hydraulic circuit comprising a pair of hydraulic pumps, each directly connected to each half of the actuators and having relatively small capacity than the above-mentioned pump of large capacity, thereby preventing the power loss as much as possible. As required, the parallel type hydraulic circuit is provided with hydraulic Pumps of variable capacity so that when a part of the actuators needs not be actuated, a hydraulic pump connected to the actuators which are not actuated is not driven, thereby preventing the power loss as much as possible. However, if the hydraulic circuit comprises a pair of main hydraulic pumps each simply connected to each corresponding half of the actuators without any cross connection with another half of actuators so that each pump provides hydraulic power to corresponding actuators, the pumps can not commonly provide hydraulic power thereof to an actuator which is overloaded resulting in requiring relatively high hydraulic power, thereby causing the overloaded actuator to be troubled. In result, the parallel type hydraulic circuit is provided with cross connections, each connecting the inlet line of an actuator connected one of the main hydraulic pumps, said actuator being to be often overloaded, with the inlet line of another actuator connected to the other pump so as to allow the hydraulic fluid from the one pump to be supplied to the other actuator cross-connected to the one actuator as the other actuator requires relatively large quantity of fluid flow due to overload thereon, thereby efficiently driving the overloaded actuator without any trouble of the main pumps.
However, simultaneously with cross-connecting the actuators, which are often overloaded, each main hydraulic pump is directly connected to its own actuators. Thus, in case of occurrence of overload on an actuator of the actuators connected to each other, a main pump directly connected thereto supplies almost of required quantity of hydraulic fluid flow to the overloaded actuator, while the other pump being cross-connected to the overloaded actuator only supplies small part of required quantity of fluid flow. In result, both hydraulic pumps can not equally provide a quantity of hydraulic fluid flow to the actuator which is overloaded, thereby causing the pump directly connected to the overloaded actuator to overly drive, resulting in occurrence of trouble thereof, but causing the other pump being cross-connected to the overloaded actuator to drive with considerable reserve. Also, each main hydraulic pump can not equally provide respective desired quantity of hydraulic fluid flow to the respective actuators connected to each main pump due to hydraulic fluid distribution characteristics according to the load thereon so that an actuator is driven at high speed while another actuator is driven at low speed. In other words, the actuating speeds of respective actuators are different from each other. In accordance, the known excavator has another disadvantages in that the hydraulic pumps are often overly driven due to unequal quantity of hydraulic fluid flow outputted from both pumps to the actuator which is often overloaded and directly connected to a pump and cross-connected to the other pump. Thus, the desired operation such as excavating operation, surface finishing operation and the like can not be efficiently carried out due to unequal distribution of the quantity of hydraulic fluid flow from each main hydraulic pump to respective actuators directly connected to the pump.
Sixth, the excavator needs pre-running for each actuator thereof before practice running in order to check the condition of the actuator, the zero point of each sensor nearly mounted to the actuator for sensing the actuating condition of the actuator and lubricating condition of each operating element, such as the boom, the dipper stick, the bucket or the like. However, the pre-running is manually carried out one by one by the operator for each actuator. Thus, the known excavator has another disadvantage in that the pre-running manually carried out one by one by the operator needs cumbersome handling of the control levers/pedals and consumption of considerable long time, and furthermore in case of occurrence of miss in checking the actuating condition of each actuator during the pre-running, a serious safety accident easily occurs such as due to trouble of the actuators.